Electrocardiography in myocardial infarction

Electrocardiography in suspected myocardial infarction has the main purpose of detecting ischemia or acute coronary injury in emergency department populations coming for symptoms of myocardial infarction (MI). Also, it can distinguish clinically different types of myocardial infarction.

Technical issues

The standard 12 lead

The 12 lead ECG is used to classify MI patients into one of three groups:[4]

1. those with ST segment elevation or new bundle branch block (suspicious for acute injury and a possible candidate for acute reperfusion therapy with thrombolytics or primary PCI),
2. those with ST segment depression or T wave inversion (suspicious for ischemia), and
3. those with a so-called non-diagnostic or normal ECG. However, a normal ECG does not rule out acute myocardial infarction.

ST elevation MI

The 2018 European Society of Cardiology/American College of Cardiology Foundation/American Heart Association/World Health Federation Universal Definition of Myocardial Infarction for the ECG diagnosis of the ST segment elevation type of acute myocardial infarction require new ST elevation at J point of at least 1mm (0.1 mV) in two contiguous leads with the cut-points: ≥1 mm in all leads other than leads V2-V3. For leads V2-V3: ≥2 mm in men ≥40 years, ≥2.5 mm in men <40 years, or ≥1.5 mm in women regardless of age. This assumes usual calibration of 1mV/10mm.

There are heavily researched clinical decision tools such as the TIMI Scores which help prognose and diagnose STEMI based on clinical data. For example, TIMI scores are frequently used to take advantage of EKG findings to prognose patients with MI symptoms.^[10] Based on symptoms and electrocardiographic findings, practitioners can differentiate between unstable angina, NSTEMI and STEMI, normally in the emergency room setting.^[11] Other calculators such as the GRACE^[12] and HEART ^[13] scores, assess other major cardiac events using electrocardiogram findings, both predicting mortality rates for 6 months and 6 weeks, respectively.^{[citation needed]}

Typical progression

Sometimes the earliest presentation of acute myocardial infarction is the hyperacute T wave, which is treated the same as ST segment elevation.^[14] In practice this is rarely seen, because it only exists for 2–30 minutes after the onset of infarction.^[15] Hyperacute T waves need to be distinguished from the peaked T waves associated with hyperkalemia.^[16]

In the first few hours the ST segments usually begin to rise.^[17] Pathological Q waves may appear within hours or may take greater than 24 hr.^[17] The T wave will generally become inverted in the first 24 hours, as the ST elevation begins to resolve.^[17]

Long term changes of ECG include persistent Q waves (in 90% of cases) and persistent inverted T waves.^[17] Persistent ST elevation is rare except in the presence of a ventricular aneurysm.^[17]

See also

• Sgarbossa's criteria

References